1. Field of the Invention
The present invention relates to power converting technology, in particular, to a power converter in Power-over-Ethernet (PoE) system and control method thereof.
2. Description of Related Art
The PoE technology can transport power and data to the corresponding electronic device through the twisted pair cable in Ethernet. The PoE technology mainly is divided into power sourcing equipment (PSE) and powered device (PD). Currently in the art, the PoE technology mainly takes two communication protocols. One PoE communication protocol is IEEE 802.3 AF. This PoE communication protocol at the PSE provides a direct-current (DC) power with a voltage of 44V to 57V and a current of about 350 mA and the PD can obtain the power of at least 12.95 W through the cable of CAT-3. Another PoE communication protocol is IEEE 802.3 AT. This PoE communication protocol can be compatible with the foregoing 802.3 AT but also provides a direct-current (DC) power with a voltage of 50V to 57V and a current of about 600 mA, and the PD can obtain the power of at least 25.5 W through the cable of CAT-5. Therefore, the PSE using IEEE 802.3 AF is called type-1 power system and the PSE using IEEE 802.3 AT is called type-2 power system. The PD can recognize the power system type used by the PSE from the input voltage.
When implementing the PoE technology, to allow the control circuit at the secondary side of transformer in the PSE to obtain that the input voltage received at the primary side of transformer is belonging to type-1 power system or type-2 power system, the optical coupler is usually taken to transmit a signal, which is used to determine as the type-1 power system or the type-2 power system, from the primary side of the transformer to the control circuit at the secondary-side. However, the optical coupler is easily broken due to the internal LED source, and manufacturers intend to take another way to implement the power converter in the PoE technology.